The XmbDrawImageString,
XwcDrawImageString and Xutf8DrawImageString functions fill a destination
rectangle with the background pixel defined in the GC and then paint the
text with the foreground pixel. The filled rectangle is the rectangle returned
to overall_logical_return by XmbTextExtents, XwcTextExtents or Xutf8TextExtents
for the same text and XFontSet.

When the XFontSet has missing charsets,
each unavailable character is drawn with the default string returned by
XCreateFontSet. The behavior for an invalid codepoint is undefined.

The
function Xutf8TextExtents is an XFree86 extension introduced in XFree86
4.0.2. Its presence is indicated by the macro X_HAVE_UTF8_STRING.